In conjunction with the National Institute of Mental Health, NIA is completing a study of senile dementia in an adult community population. A contract has been awarded to Yale University to survey a sample of the New Haven, Connecticut adult population for this purpose. NIA is specifically interested in defining the occurrence of senile dementia in persons 65 years of age and older. The study will consist of a household interview and a follow-up of all subjects. A questionnaire has been developed by the investigators.